The present invention relates to the storage of a coolant fluid comprising two phases of one and the same substance in melting equilibrium, for example water to which an antifreeze agent such as salt, alcohol, ethylene glycol or propylene glycol is added. This substance in melting equilibrium may also be an eutectic. The coolant fluids considered according to the invention are then obtained, transported and used in diphasic form (liquid phase plus solid phase), in particular in a homogenous consistency close to that of water-ice.